nickstenning/mail-backup repository overview

⁠Azure mail backup

This repository contains the tools and configuration for my automatic mail backup system.

For years I've synced my mail to a local Maildir⁠ using the wonderful OfflineIMAP⁠. This Maildir is also a git repository, which allows me to reproduce the state of my mailbox at any point in the past, and gives me a great deal of confidence that none of the backup tooling will accidentally lose email.

Until recently, this setup has been running on a VM in Linode⁠ which was up 24/7/365. This repository contains the code necessary to set up a VM in Azure which serves the same purpose and runs only when needed.

⁠Design

The git repository is stored on a Azure Managed Disk⁠, which is attached to a VM.

The VM is booted once an hour by an Azure Function on a Timer trigger⁠. On boot, it fetches the latest updates from my mail account and writes them to the git repository. When it's done, it shuts down. This whole process typically takes less than 2 minutes, which means the VM only runs for about 24h in a month.

There are three components to this setup stored in this repository:

1. docker/: A Docker image containing OfflineIMAP⁠ and a script to manage the git repo.
2. function/: The source of an Azure Function to periodically boot the VM.
3. createvm: A script which uses the Azure CLI⁠ to create and configure an appropriate VM. You should create a resource group and managed disk by hand (i.e. through the Azure Portal) before running createvm.

⁠Costs

createvm will set up a Standard_B2s VM. Running one of these for 24h costs just over $1 as of August 2019, so I expect this setup to run about $1/month in compute costs.

Additional costs apply for the managed data disk and the OS disk. The default OS disk will cost $5.28/mo.

⁠How to use this

Here's a rough outline of how to adapt this setup for yourself:

1. Create a resource group and a managed disk within that resource group.

2. Run createvm.

3. Connect to the VM and follow the instructions in /opt/mailbackup/README.

4. Set up an Azure Function App using the code in function/.

5. Enable the system assigned managed identity for the function app (see the "Identity" tab) and grant that identity the "Contributor" role on the resource group you created in step 1.

   (You may be able to get away with more restrictive permissions -- it needs the ability to list resources in the resource group and start a VM.)

6. Configure the Function App: you'll need to set the VM_RESOURCE_GROUP setting to the name of the resource group in which you created the VM.

Note that you'll certainly need to edit /opt/mailbackup/etc/offlineimaprc.template and /opt/mailbackup/etc/docker.env on the VM to suit your needs.

⁠License

Everything in this repository is shared without warranty under the terms of the 3-Clause BSD License, a copy of which is provided in LICENSE.